(a) Field of the Invention
The present invention concerns the production of a controlled atmosphere for the heat treatment of metals in at least one treatment oven or vessel, the atmosphere consisting essentially of inert or reducing gases which are either pure or in mixture. More particularly, the invention is directed to a process for the production of a controlled atmosphere which is substantially free of oxidizing gases.
The present invention can be applied to the production of controlled, heated protective atmospheres adapted for heat treatments, such annealing, heating after hardening, sintering and brazing, for coating operations by deposition onto hardened articles, such as galvanizing and aluminizing, for the production of metals which are very sensitive to oxidation, such as titanium, zirconium and aluminum-lithium alloys, or for the co-sintering of multilayered ceramics and metals, or the binding of ceramics and metals. These controlled atmospheres are used at varying pressures ranging from 10.sup.-3 Pa to 10.sup.8 Pa (absolute pressure) depending on the type of vessel utilized for the treatment.
(b) Description of Prior Art
Controlled atmospheres are generally produced starting from industrial gases or exothermic or endothermic generators gases and typically they consist mainly of inert gases, such as nitrogen, argon or helium, and/or of reducing gases, such as hydrogen or carbon monoxide, which are either pure or in mixture. In order to produce a controlled atmosphere in a vessel, these gases are injected into the vessel under a flow sufficient to minimize the content of residual oxidizing gases, such as water vapor, carbon dioxide and/or oxygen. To prevent oxidation, and considering the modifications of the chemical composition of the products treated or produced under such controlled atmospheres, it is necessary that the controlled atmospheres be inert, eventually reducing with respect to the metal under consideration or sufficiently weakly oxidizing to prevent a significant oxidation from occurring during the treatment. However, trace amounts of oxidizing gases, such as H.sub.2 O and O.sub.2, remain in the controlled atmosphere due to micro-leaks in the gas conduit systems or in the treatment vessel, of continuous or discontinuous feed materials or articles charged in the treatment vessel, resulting in air entries which are disastrous to the controlled atmospheres in terms of quality, in wrong handling of the gas system, of the surface condition of the articles to be treated or of their degassing during their heating.